Confusion over aperture

[james_marchant]

I am new at SLR photography, and photography overall, so this may not be the

correct place to ask this but I recently bought a Canon EOS 400d (Rebel XTi in

the USA) and I bought the lens kit with it (saving up for a better lens now but

needed one with the camera). The confusion is that the lans says f/4.0-5.6 but

the aperture that the camera says it is using varies from 4.0 up to almost 11.0

sometimes. Does the camera body also have the ability to change the aperture and

the lens only defines the maximum aperture? Or is it something else?

 

Thanks for any help.

[rainer_t]

-- "f/4.0-5.6"

 

Sounds like you bought the EFS 17-85/4-5.6 IS USM with your camera.

 

-- "but the aperture that the camera says it is using varies from 4.0 up to almost 11.0 sometimes."

 

f/4 is the maximum aperture of the lens at 17mm, f/5.6 is the maximum aperture at 85mm. None of these numbers is the minimum aperture (which is btw even smaller than f/11 ... its more like f/22 or so).

 

-- "Does the camera body also have the ability to change the aperture"

 

Yes, certainly.

 

-- "and the lens only defines the maximum aperture?"

 

By its construction, the lens defines its maximum and also its minimum aperture at the different focal lengthes. The camerabody is free to choose any aperture value available.

[colinsouthern]

James Marchant wrote: <i>Does the camera body also have the ability to change the aperture and the lens only defines the maximum aperture?</i><p>

 

Hi James<p>

You got it in one :)

[peterlyons]

The numbers on your lens indicate the MAXIMUM aperture. At your widest focal length, you

can go as wide as f/4. At the longest, you can go as wide as 5.6. Smaller apertures,

probably down to f22 or f32, are available at all focal lengths. The maximum aperture is

noted on lenses because it says so much about the light-gathering ability, and the cost, of

the lens.

[james_marchant]

Wow thanks for the speedy replies! I was thinking of checking back in a day or two but check back 30 minutes later and 3 excellent responses! That all makes more sense to me now.

 

Another question which may be a little of topic; I keep reading about the 400D's magnification ratio (its name varies) which muliplies the focal length by 1.6? Does it do this to all lenses? If I were to buy a 28mm lens would it push it from the wide-angle region into the normal lens region?

[leopoldstotch]

In response to your second question, yes. Because the sensor of your camera is smaller than a 35mm frame, lenses become the <i>equivalent</i> of 1.6x their focal length. And yes, a 28mm lens does become normal when mounted on a 400D. Note to everyone else: I italicized "equivalent" for a reason. Don't start another one of those reach arguments.

[ronaldo_r]

James - you should learn basics about photography (read something) before posting such basic questions. I mean your questions Are TOO basic to be respectful to this forum. E.g, it's like posting to a car forum asking the purpose of the clutch pedal. I think that'll be disrespectful.

 

I had to ask myself the same questions about aperture etc when I was learning, however a 5-second google would've helped to frame your question in a more useful - to you - way.

[William Michael]

I was pretty relaxed with the first and also the follow up question from Mr Marchant.

 

I encourage him to reads books, and learn the search mechanics here.

 

But writing purely as a PAYING member of Photonet, I felt he showed me no disrespect to me whatsoever.

 

WW

[keith_lubow]

Perhaps if there were a dedicated forum for questions like this, we wouldn't find so many of them in the equipment forums, where they do not belong. Nonetheless, given the lack of such a forum, I don't know where else I would have posted the question myself.

 

James; there is nothing wrong or disrespectful about asking. It's just that it shows that you have obviously not done any very basic learning on your own, which is quite aggravating to most of the people who answer questions on the internet.

 

Your questions would be answered within a week or two in any photography class and/or in any basic photography text. Getting SUCH basic information from a message board is not the best or most efficient way to learn about this stuff.

 

Keith

[ronaldo_r]

Don't worry William, I've paid PN, they got my money, I'm not a freeloader. However that mmebership was cancelled by them and they refused to refund. So there, they can cancel my current one as well, see if I care. But I've already paid them, just like you did

[colinsouthern]

I'm not sure how many others I speak for, but personally, I have no problems with these types of questions what-so-ever.

 

For goodness sake - we're supposed to be here to help - to solve problems for people - and to make them feel welcome. If the problem comes in the form of something simple or something complicated, who cares? - they're ALL important to the people we're trying to help, and that's the most important thing by far.

 

If some don't like it, the solution is simple - choose another topic to help with that's more to your liking and leave the easier stuff to others.

[leopoldstotch]

I'm with Colin on this one. He took the words right out of my mouth. If you don't like thses posts, don't respond. Besides, I much prefer these over the "What are thses spots in my picture" or "can I use my FD lenses on EOS" questions.

[chrisjb]

I have no problems to help with the most simple questions, 1st of the search can be a lesson on its own and some folks may be totally isolated from a place of learning. Myself as many others have been shooting over 4 decades, What I enjoy with this forum is seeing younger folks passing on previous answers. IMO teaching others is a good way to learn. Once basics is learnt finding new information becomes easier

 

my 02c

[colinsouthern]

Unlike many of you, I haven't been shooting for "many decades" - and I still remember all too well trying to figure out what I needed to do with my aperture to increase or decrease my depth of field. I also remember all too well the help, but more often than not hinderance I received from many on USENET. This site is different - this is the first site I've come across where there's always an answer to the question - but even when people don't agree (which is also quite common) it NEVER resorts to mud-slinging and name calling.

 

Because of the patience and wisdom of good folks here I've learned a lot - and most not even with the questions I've asked - and I'd like to think I've helped a few others along the way too.

 

For me the most important thing of all is to just help people - I'm sure that when we do that we ultimately end up helping ourselves just as much.

[William Michael]

To Ronaldo R:

 

No, I am not worried about the payment thing at all.

 

I was me having a cheap swipe at you: that might be judged right or wrong, but mostly it was wrong.

 

I swung at you because I considered you were being nasty to a new bloke on then block. And for that cheap swipe, you have my apology.

 

But I do find your statement about your membership more interesting than you might imagine, considering I seemingly have upset some in power at Photonet.

 

On the original issue, I do stand by my point: I do not think posting the question was disrespectful.

 

Really, it is ?learn the rules as you go? here, and asking questions is the first step to learning the rules.

 

Embracing and polite answers are more helpful than those using negative words.

 

Regards,

 

Bill

[William Michael]

>>> and I still remember all too well trying to figure out what I needed to do with my aperture to increase or decrease my depth of field. <<<

 

 

Huh?

 

Are they related?

 

:)

 

... and hopefully we can have a laugh as well.

[mike dixon]

<i>But I do find your statement about your membership more interesting than you might imagine, considering I seemingly have upset some in power at Photonet. </i><P>

To my knowledge, the only situation in which a subscriber would lose his "membership" without a refund is if he were banned from the site. Having an occasional post removed doesn't mean you're at risk if you're a generally helpful and considerate user. Banning generally occurs only after repeated suspensions and a clearly-demonstrated desire to disrupt the site. I suspect that "Ronaldo R." is an account set up by someone who was previously banned. Considering the number of times Ronaldo has had posts removed and has been suspended from various forums, he seems destined to repeat his past performance.

[ben_goren]

James, if you're still reading, here's a very quick primer on focal lengths and crop factors.

 

The easiest way for a photographer to understand the focal length of a lens is to cut a hole

in a piece of cardboard (paper, etc.) the same size as the film / sensor of the camera.

Then, hold that hole the same distance from the eye as the focal length of the lens -- say,

two inches for a 50mm lens. What you see through that hole is what'll get imaged.

 

Two factors change the ``zoom'' of such a system: the size of the hole (smaller hole =

``longer'' zoom) and the focal length (farther away = ``longer'' zoom).

 

The sensor is a bit smaller than half the size of a piece of 35mm film (``135 format''), and

so it ``magnifies'' things by a bit more than 1.5 times (1.59, to be precise). You could get

the exact same ``magnification'' by taking a picture with a 35mm camera (or a ``full-

frame'' camera like the 5D or 1DS) and cutting away the sides until you were left with an

area the same size as the sensor in the 400D.

 

The attached image should help put the relative sensor sizes in perspective.

 

Cheers,

 

b&

[ben_goren]

I suppose, if I've gone this far, I might as well explain f/ numbers, as well. They're pretty

trivial: they're just the ratio of the focal length of the lens to the physical diameter of the

aperture. (Not really, but close enough.) A 50mm lens at f/2.0 has a 25mm aperture --

about an inch. Stop the lens down to f/4.0, and the aperture now measures 12.5mm

across.

 

The way the geometry works out, if you multiply the aperture by the square root of two

(1.4 is the common approximation), you cut the light hitting the sensor in half. An

aperture of f/2.0 lets in twice as much light as an aperture of f/2.8, for example.

 

The wider the aperture, the narrower the zone of sharp focus. If you play around drawing

some diagrams of a two-dimensional lens, and compare the possible angles for light rays

coming from a point source to reach the sensor, you'll figure out that there's a larger area

for a larger aperture, meaning that the light gets spread out farther and therefore

becomes fuzzier and more diffuse. This can be used to good effect, and it can also be a

cause of great headache.

 

With the shutter speed, exposure is a direct relationship. An exposure of 1/30 seconds

lets in half as much light as an exposure of 1/15 seconds. The slower the exposure, the

more things in the scene will move, and therefore the blurrier they will become. As with

aperture, it's something you need to be aware of and control in order to get the results

you want.

 

The last piece of the puzzle is the ``speed'' of the sensor / film, measured in ISO

numbers. Double the number, and you double the sensitivity of the sensor / film to light,

just as if you had slowed down the shutter by half or opened up the aperture by 1.4x. The

downside is that you also increase the grain or noise by doing so; the sensor / film doesn't

work as efficiently and essentially makes stuff up. There are times when this effect is

desirable, but they're few and far between. For the most part, you want to know what kind

of noise to expect at a given ISO (by experimenting, of course), and decide what does and

doesn't work for you.

 

There -- that should keep you busy for a while....

 

Cheers,

 

b&

[ronaldo_r]

Ban me. I don't care. Innocent people get shot and deported. Being banned from PN is nothing.

 

William, I accept your point. However, I still believe there's a thin line between the desire to learn and being lazy. And I find laziness disrespectful.

 

By the way, most questions that fall under the category "there's no such thing as a silly question" aren't silly at all. Usually such 'silly' questions are a result of educational effort that presented a paradox requiring a second opinion.

 

Asking "what's aperture" without making a slightest attempt at learning (or even reading the camera's manual) is lazy, offensive and disrespectful - TO ME.

[William Michael]

To Mike Dixon:

 

I find your comment insightful and thoughtful, apropos my personal frustration, (in regard to another forum).

 

Thank you for taking the time and effort to post it.

 

To Ronaldo R:

 

I respect and uphold you right to voice you view; but I do not agree with the stance you take, nor agree with your delivery method.

 

To James Marchant:

 

In my opinion, go on asking as many sincere questions, as you like.

 

WW

[jacob_brown]

"Ban me. I don't care. Innocent people get shot and deported. Being banned from PN is nothing."

 

So this explains your constant trolling. Ah.

[ellis_cory1]

Ronaldo, we all learn in different ways and some of us are just as confused after reading the manual as before. We need someone to start where we are and lead us in the right direction, rather than read a set text. Others need to be shown 'how to' and still others experiment and see what happens. I agree with those who say all questions, simple or complex are OK, after all, sometimes the simple ones hide a more complex point !

ATB

Ellis

[jim_b5]

Hello everyone,

 

I learn so much from answers to "obvious" or "simple" questions that I don't have to post the questions myself.

 

A big thank you to all the patrons of Photo Net that make the effort to share their knowledge.

 

Well done.

[james_marchant]

Firstly, let me say that I never asked, or at least I never intended it to be interpreted as, "What is aperture?"; I understood this and the basics of f-stops, etc, by doing research as you have said. My confusion arose when looking at lenses because as I said the lens read "f/4.0-5.6" yet the aperture the camera said it was using was in the range 4.0-11.0. This seemed contradictory and searching for numerous things via google such as "lens terminology", "glossary pf lens terms", "lenses and f-values" returned the definitions I had already learnt but still didn't answer my question as to why the two objects seemed to disagree as none of them said that the f-values given on lenses are the maximum they can obtain rather than the range they can obtain. So I decided to ask people who knew more than me on the subject and a search of "photography forums" took me here. I apologise if you feel that I was disrespectful but everyone has to start somewhere and even a simple question for someone semi-experienced can seem like an impossible research task for someone who is new; having always used point-and-shoot cameras I easily class myself as new. The research I did could not answer the question I had after an hour or so, so seeking help was the next step. Thank you to everyone who has answered; I have a basic knowledge of terminology but as to how these necessarily relate, clarification or even just tuition are always helpful. Everyone learns differently and everyone has to start somewhere.